1. Field of the Invention
The invention relates to methods and apparatus for reclamation of cellulosic fiber materials and more particularly concerns the conversion of waste papers to cellulosic fiber pulp.
2. Brief Description of the Prior Art
Paper stock from reclaimed waste papers comprises the second largest source of fibrous raw material for paper making after wood pulps. Reclaimed waste paper is of great interest as a means of saving our natural resources and for reducing the impact of waste paper on the ecology. Although numerous methods and devices have been developed to convert waste papers to usable fibrous pulps, most depend on careful segregation and classification of the waste materials to obtain clean, high quality pulps. However, waste papers are generally delivered to the paper mills from a wide variety of sources. The lots of waste paper are of varying fibrous constituency and contain indeterminate and widely varying quantities of groundwood in the papers. In addition, the papers often carry widely varying amounts and kinds of resins, metallic foils, dyes, inks, sizing, metallic fasteners, adhesives, fillers, binding cords and like contaminants. Careful sorting, classification and segregation of the delivered waste in an onerous if not impossible task. Accordingly, there exists a need for apparatus and methods of taking unsorted, unsegregated, mixed paper materials including unwanted contaminants and processing the same into high grade fibrous pulps.
Heretofore, apparatus was available which had the capability of processing unsorted and mixed lots of waste papers in the preparation of fibrous pulps; see for example the disclosure of U.S. Pat. No. 3,844,488. Such apparatus generally comprises a slusher, a fiberizer - (or also called pulper or grader) operated under pressure and a variety of sieves and holding tanks. In operation, the unsorted papers are slushed in the slusher wherein many of the gross contaminants such as wires and metallic fasteners are separated. The slush is then carried to the pressurized fiberizer for further separation of the contaminants and fiber liberation. After a period of slushing and fiberizing the resulting pulp is sieved and processed further. One of the problems associated with the prior art methods and apparatus concerns the difficulty of separating the liberated fibers from the contaminants. For example, there is a tendency for the relatively heavy contaminants to entrain substantial proportions of partially liberated fibrous materials. Upon separation of heavy contaminants from the pressurized fiberizer, substantial amounts of fibrous materials are lost from the fiberizer and consequently from the product pulp. It has been estimated that from 10 to 20 percent by weight of fibrous material is lost from the product pulp in this manner. Previously it was sought to solve this problem by recirculating the heavy contaminants through the fiberizer or by increasing the residence time of the heavy contaminants in the fiberizer to effect a greater separation of the entrained fibrous materials. The disadvantage of these approaches resides in the additional wear and tear on the fiberizer caused by the prolonged presence of the heavy contaminants therein.
The above described problems of the prior art are solved by the apparatus and method of my invention. The apparatus and method of the invention provide a highly efficient means of processing grossly contaminated waste papers into high quality, cellulosic fiber pulps with a high proportion of unbroken fibers, in near quantitative yields.